1. Field of the Invention
The present invention relates to a method for inhibiting hydration of clays in drilling operations comprising the use of an aqueous based drilling fluid containing clay hydration inhibitors for the drilling industry, that is to products which are effective for the inhibition of swelling of clays (also called shales) which come into contact with the fluids used in the drilling and construction of oil and gas wells for the petroleum industry. The clay hydration inhibitors (also called clay inhibitors or hydration inhibitors) of the invention are bis-hexamethylene-triamine and the salts thereof.
2. Background of the Art
In the rotary drilling of wells a drilling fluid circulates throughout the underground well to carry the cuttings from the bit and to transport these cuttings to the surface. Contemporaneously, the drilling fluid cools and cleans the drill bit, as well as it reduces the friction between the drill string and the drilled hole, and it also stabilizes the uncased sections of the well. Usually the drilling fluids form a low permeability filter cake in order to seal any permeability associated with the surrounding geological formations.
The drilling fluids may be classified according to their fluid base: oil based fluids which contain solid particles suspended in an oil continuous phase and, possibly, water or brine may be emulsified with the oil. Alternatively, water base fluids contain solid particles suspended in water or brine. Various other components may be added, deliberately or otherwise, to water based drilling fluids: a) organic or inorganic colloids, such as clays, used to impart viscosity and filtration properties; b) soluble salts or insoluble inorganic minerals used to increase the fluid density; c) other optional components may be added to impart desirable properties, such as dispersants, lubricants, corrosion inhibitors, defoamers or surfactants; d) during the drilling operations formation solids may disperse into the drilling fluid.
Formation solids that become dispersed in a drilling fluid include cuttings from drilling and soil and solids from the surrounding unstable formation. When the formation yields solids that are clay minerals which swell, this can potentially compromise drilling time and increase costs. Clays are typically composed of sheets that can have exposed surface hydroxyls. Multivalent atoms may create a negative potential at the clay surface and, in this case, cations can be adsorbed onto the surface. These cations may be exchangeable. Substitutions within the clay structure and the presence of exchangeable cations affect the tendency of the clay to swell in water. For example surface hydration gives swelling with water molecules adsorbed on clay surfaces. All types of clays can swell in this manner.
Another type of swelling is called osmotic swelling, when the interlayer ion concentration leaches water between the clay unit layers, swelling the clay. Only some clays can undergo osmotic swelling. All types of clay swelling can cause a series of problems. This increases drag between the drill string and the sides of the borehole. This can cause the loss of fluid circulation and sticking of the drill string and bit.
This is why the development of effective clay swelling inhibitors is important to the oil and gas exploration industry. The present invention works towards a solution to these difficulties. Many clay inhibitors are known, including the use of inorganic salts such as potassium chloride, which effectively inhibit clay swelling and which are well known to those skilled in the art. Numerous patents have been filed which describe techniques or products which can be used to inhibit clay swelling. Without completely summarizing the patent literature, and by way of example, we can cite the inhibitor compositions based on: a) inorganic phosphates, described in U.S. Pat. No. 4,605,068 (YOUNG et al.); b) polyalkoxy diamines and their salts, in U.S. Pat. No. 6,484,821, U.S. Pat. No. 6,609,578, U.S. Pat. No. 6,247,543 and US 20030106718, all by Patel at al.; c) choline derivatives in U.S. Pat. No. 5,908,814 (PATEL et al.); d) oligomethylene diamines and their salts, in U.S. Pat. No. 5,771,971 (HORTON et al.) and US 20020155956 (CHAMBERLAIN et al.). In particular U.S. Pat. No. 5,771,971 describes the use of diamines with a chain length of 8 or less, but does not mention the use of organic triamines.
US 2007/0207932 (MERLI et al.) relates to a method for inhibiting hydration of clays in drilling operations comprising the use of an aqueous based drilling fluid containing 1,2-cyclohexanediamine and/or its salts.